1. Field
The present invention relates to ways to generate energy by harnessing, transducing, extracting or otherwise converting the kinetic energy of a flowing fluid, including flowing air currents (including wind currents) and flowing water currents (including ocean currents, for example tidal currents, and watercourse currents, for example river currents). In this document, in the absence of contrary indication, the words generate, harness, transduce, extract and convert, in all their various forms, will be used interchangeably.
2. Description of Related Art
Terrestrial wind turbines have shown considerable success; however, they have many shortcomings. They are costly to build and deploy and are prone to damage under severe wind conditions. Their massive size and noisiness make them unattractive to some people. Some people have expressed concerns that such turbines present a health hazard to people and birds, that they affect local weather patterns and that they may affect farming. These concerns are prompting increasingly large and much more expensive offshore deployment of wind turbines.
Nevertheless, the success enjoyed by wind turbines, when the air currents are blowing just right, has enticed some to directly apply this concept to water current energy retrieval. This conventional reasoning suggests that because the density of water is about 800 times greater than that of air, therefore the concentration of energy must also be that much greater, resulting in the need for a much smaller device to extract the same energy. Unfortunately, many popular designs have focused on this oversimplified analogy, ignoring other forces that come into play. One must even be careful in applying concepts drawn from penstock-fed hydraulic turbines in hydroelectric systems.
Installing a water generator submerged in a water flow, for example a tidal current, exposes the generator to uneven and very significant forces, with water being 800 times denser than air. This is the case whether we use a vertical axis or a horizontal axis of rotation. These uneven forces, plus the resistive forces encountered by rotating vanes trying to cut through the dense water medium, have resulted in failures to apparently very substantial devices, thus providing power outputs that pale in comparison to the predicted ratings.
Thus for example, a tidal current stream is typically very slow, relatively speaking, and the water immediately beyond the turbine blades is still present in full force to slow down the turbine rotation. This resistive force, slowing down the envisioned turbine rotation, is almost as great as the forward force of the tidal current that conventional wisdom is attempting to utilize. To illustrate, if we manually or mechanically attempted to spin the turbine at the expected running speed, and while the tidal current speed is nil, we would discover that the required energy is absolutely immense. Almost all of this required energy, or drag, would have to be overcome by the forward force of the tidal current, not to mention what additional energy is required to drive a power take-off to provide the expected power output.
In a hydraulic system, the water stream in the penstock travels at a considerable speed when it reaches the turbine, dependent on the vertical drop, and the turbine spins accordingly fast. The water stream immediately beyond the hydraulic turbine continues to drop and is on the verge of creating cavitations. What this means is that the downstream side of the hydraulic turbine does not have to slice its way through the dense water medium. There is minimal drag, or energy loss. In essence, the turbine spins freely with respect to the downstream side, and is relatively unencumbered.
A similar environment besets a wind turbine. When there is no wind blowing, and if we attempted to rotate the turbine at the rotational speed of operation, we would likewise find that the required energy is immense. Almost all of this required energy, or drag, would have to be overcome by the forward force of the wind, not to mention what additional energy is required to drive a power take-off to provide the expected power output.
There are several tidal current turbines being tested, and we read about their unexpected failures, or we hear nothing about the low and unpublished results. All the blades are torn off one machine, while another is retrieved to prevent total destruction. And so the story goes, with the expected power output of those that have survived being unreachable, being unexpectedly low and/or unpublished.
Devices like waterwheels are caused to operate by the weight of falling water at the circumference of the wheel. Others may be caused to operate by the force of the flowing water on the lower submerged portion of the wheel. In this case the effective lateral force relates directly to the point on the circumference and its submergence. The force is not uniform over the arc of submergence, because the force is strictly lateral acting on a circular and revolving member.
Paddle boats have similar limitations. In this case, for balanced drive, there is a wheel on both sides of the boat. Regardless, the force coming from the engine room is not uniformly applied in the lateral dimension. When the wheel first touches the waterline, a portion of the applied force is downward and is wasted, as it is when the wheel approaches emergence from the water medium, a portion of the applied force is upward and is likewise wasted. The most efficient application of the applied force is at the point where it impacts on the perpendicular radius to the direction of flow.
The rotational force over a lateral distance, described above, is not as efficient as a lateral force over the same distance. Further, none of these applications above can match a continuous lateral force over an identical distance.
Accordingly, what is needed is a better way to capture the almost limitless green-house-gas-emissions-free renewable and sustainable energy, at a lower cost in capital investment, operations and maintenance and with increased energy capture per ton of fabricated material.